Prior art includes Swiss Patent 581 377. There, an overcurrent limiter or a PTC resistor component is disclosed, in which 3 PTC resistors with different dimensions and that are made from sintered bodies may be connected in parallel with one another and respond to each other consecutively when a short-circuit current occurs. These PTC resistors may also be connected in parallel to one another with a fixed resistor and a switch. Such overcurrent limiters are able to reversibly limit short-circuit currents to values below the limit that is destructive for the active components, for example converters. During a malfunction, the PTC resistor is heated to a temperature above its response temperature and limits the short-circuit current to values that are non-damaging for the current circuit. The thermal destruction of the PTC resistor is prevented by commutating the short-circuit current to the parallel resistor.
It would be desirable for the converter operation that the intermediate circuit inductance during nominal operation be distinctly reduced. In the case of a short circuit however, the expected short-circuit current amplitudes rise to values that currently cannot be controlled in traction systems. Since the required reaction times of the protective device are in the .mu.s range, a current limiter is indispensable. But the intrinsic inductance of the known current limiter is too high. Intrinsic inductance values in the nH range are required.
Regarding the relevant prior art, reference is made to EP 0 548 606 A2 which specifies an overcurrent limiter that has a varistor connected in parallel with a PTC resistor and that may be combined with the PTC resistor in one component.
The softcover book Elektrotechnik, Band 3, Bauelemente und Bausteine der Informationstechnik, Editor Prof. Dr. E. Phillipow, 1st edition, VEB Verlag Technik, Berlin, 1978, p. 250 describes winding designs for low-inductance resistors, e.g. the bifilar winding, the Chaperon winding, and the meander shape.
It is known from U.S. Pat. No. 1,146,592, for producing precision resistors for Wheatstone bridges, to arrange at least two low-inductance, bifilar or spiral standard resistors in parallel connected, electrically insulated resistor branches in identical track areas on top of one another. Partial currents then flow through these resistors branches in opposite directions, so that inductive effects of the resistor tracks connected parallel to one another compensate for one another. This kind of precision resistor is unsuitable as an overcurrent limiter. No further details are provided as to the distance between the resistor tracks connected parallel to one another.